Antenna device and transmitting/receiving device

ABSTRACT

An antenna apparatus includes two circular waveguides including a fixed-side circular waveguide and a rotation-side circular waveguide, each having a propagation mode in a TM01 mode, and being arranged coaxially with each other while a waveguide-side choke is provided between the two waveguides. A rectangular waveguide is connected to the fixed-side circular waveguide. Thereby, the high-frequency signal fed from the rectangular waveguide to the fixed-side circular waveguide can be radiated from a primary radiator to which the rotation-side circular waveguide is connected. While the circular waveguides and the waveguide-side choke can constitute a rotary joint, by rotating the primary radiator together with the rotation-side circular waveguide, scanning can be carried out with a high-frequency signal radiated from the primary radiator.

This application is a 371 of PCT/JP03/10282 filed Aug. 13, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna apparatus that is suitablefor use in scanning with high-frequency electromagnetic waves(high-frequency signals), such as micro waves and millimeter waves, overa predetermined angular range, and a transmitter/receiver, such as aradar and a communication apparatus, including such an antennaapparatus.

2. Description of the Related Art

In general, various kinds of beam-scanning antenna apparatuses used foran on-vehicle radar, for example, are known. For example, a firstconventional technique involves the use of a reciprocal first dielectricline and a second fixed dielectric line which constitute a directionalcoupler, and the first dielectric line has a primary radiator connectedto move with the reciprocal first dielectric line (Japanese UnexaminedPatent Application Publication No. 2001-217634, for example).

Also, a second conventional technique involves the use of a reflectionplate for reflecting a beam radiated from the primary radiator, whichreflection plate is rotated in accordance with the beam scanning angleusing a rotation mechanism, and an antenna transmitter/receiverincluding the primary radiator is capable of beam scanning using a cammechanism or a link mechanism (Japanese Unexamined Patent ApplicationPublication No. 11-27036, Japanese Unexamined Patent ApplicationPublication No. 11-38132, for example).

Furthermore, a third conventional technique involves a dielectric discprovided in front of a transmitter/receiver antenna having thicknessesthat differ with a circumferential angle, being rotated, and a hollowdielectric cylinder with an inclined axis arranged around a waveguideslot array being rotated (Japanese Unexamined Patent ApplicationPublication No. 10-300848, Japanese Unexamined Patent ApplicationPublication No. 6-334426, for example).

However, in the antenna apparatus according to the first conventionaltechnique mentioned above, in addition to the necessity for a reciprocalmechanism, such as a linear motor, for reciprocating the primaryradiator, etc., it is necessary to accelerate/decelerate the primaryradiator, etc., along with the reciprocation of the primary radiator, sothat the increased mechanical load on the reciprocal mechanism becomes aproblem.

Also, in the second conventional technique, the cam mechanism and thelink mechanism required for beam scanning are mechanically complicated,so that the entire antenna apparatus is liable to increase in size, andthe layout of the entire antenna apparatus is complicated because of thearrangement of the cam mechanism, thereby increasing manufacturing cost.

Furthermore, in the third technique, by rotating the dielectric disc orthe dielectric cylinder, the direction of a beam passing through thedielectric cylinder is changed. However, since the direction of theprimary radiator is not directly changed, the dielectric cylinder tendsto increase in size. Hence, there arises a problem in that the load on amotor or the like for rotating the dielectric cylinder is increased,thereby reducing reliability and durability.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide an antenna apparatus and atransmitter/receiver capable of reducing a mechanical load as well asmanufacturing cost by simplifying a structure.

An antenna apparatus according to a preferred embodiment of the presentinvention includes a fixed-side transmission line having an electricfield distribution or a magnetic field distribution that is axiallysymmetrical in a propagating direction, a rotation-side transmissionline, having an axially symmetrical electric field distribution ormagnetic field distribution, arranged coaxially with the fixed-sidetransmission line so as to be rotatable about the axis of the fixed-sidetransmission line, a transmission-line side choke disposed between thefixed-side transmission line and the rotation-side transmission line forcausing a short-circuit between both the lines at a high frequency, anda primary radiator disposed in the rotation-side transmission line so asto be rotatable together with the rotation-side transmission line forradiating high-frequency signals that have passed through therotation-side transmission line in a direction that is different fromthat of the rotation axis of the rotation-side transmission line.

With such a unique structure and arrangement, the fixed-sidetransmission line is arranged coaxially with the rotation-sidetransmission line, and both the lines have an axially symmetricalelectric field distribution or magnetic field distribution, so thathigh-frequency signals in the same mode can be propagated through thefixed-side transmission line and the rotation-side transmission lineregardless of the rotational displacement of the rotation-sidetransmission line. Between the fixed-side transmission line and therotation-side transmission line, the transmission-line side choke isprovided, so that both the lines can be choke-coupled together andshort-circuited at a high-frequency via the transmission-line side chokeso as to prevent the high-frequency signal from leaking from the gapbetween both the lines.

Furthermore, the rotation-side transmission line is provided with theprimary radiator radiating high-frequency signals in a direction that isdifferent from the rotation axis, so that by using the primary radiator,the high-frequency signal can be radiated in a direction such as asubstantially perpendicular direction and a direction inclined by apredetermined angle relative to the radiating direction of therotation-side transmission line. Also, since the primary radiator isrotated together with the rotation-side transmission line, the entirecircumstance can be scanned with high-frequency signals about therotation axis while the high-frequency signals can be radiated over anarbitrary angular range through the primary radiator by blocking anunnecessary radiation range as long as the range is within 360° (wholecircumference). When the antenna apparatus according to a preferredembodiment of the present invention is applied to a radar, for example,while wide angle detection is possible over the whole circumference,angular resolution can be improved because of the detection at anarbitrary angle.

According to a preferred embodiment of the present invention, aplurality of the primary radiators are provided in the rotation-sidetransmission line, and the plurality of the primary radiators arearranged to be directed in directions that are different from eachother.

Therefore, a plurality of primary radiators can be radially arrangedabout the rotation axis. At this time, when the primary radiatorsdirected in a predetermined direction in the plurality of rotatingprimary radiators are radiated while residual primary radiators areblocked, while the rotation-side transmission line is making onerevolution, a plurality of the primary radiators are directed in apredetermined direction. As a result, in comparison with the singleprimary radiator attached thereto, a period of time radiating thehigh-frequency signals in a predetermined direction within onerevolution can be increased so as to increase the detection period andcommunication period.

Moreover, according to a preferred embodiment of the present invention,a casing is arranged around the plurality of the primary radiators forsurrounding the primary radiators, and the casing is provided with aradiator opening formed thereon, to which any one of the plurality ofrotating primary radiators is sequentially connected.

Thereby, while high-frequency signals are radiated through the radiatoropening of the casing from one primary radiator sequentially connectedthereto, residual primary radiators are surrounded by the casing so thatthe radiation of the high-frequency signals can be blocked. Since whilethe rotation-side transmission line is making one revolution, aplurality of the primary radiators are sequentially connected to theradiator opening, in comparison with the single primary radiatorattached thereto, a period of time radiating the high-frequency signalsthrough the radiator opening within one revolution of the rotation-sidetransmission line can be increased so as to increase the detectionperiod and communication period.

Moreover, according to a preferred embodiment of the present invention,a radiator-side choke is provided between the plurality of primaryradiators and the casing, and when one of the primary radiators isconnected to the radiator opening, the residual primary radiators andthe casing are shorted therebetween by the radiator-side choke at highfrequency.

Thereby, while one primary radiator is radiating high-frequency signalsthrough the radiator opening, the high-frequency signals can beprevented from leaking through between the residual primary radiatorsand the casing, so that the loss of the entire antenna apparatus can beminimized.

According to a preferred embodiment of the present invention, an antennaapparatus includes a fixed-side transmission line having an electricfield distribution or a magnetic field distribution axially symmetricalin a propagating direction, a rotation-side transmission line, having anaxially symmetrical electric field distribution or magnetic fielddistribution, arranged coaxially with the fixed-side transmission lineso as to be rotatable about the axis of the fixed-side transmissionline, a transmission-line side choke disposed between the fixed-sidetransmission line and the rotation-side transmission line for causing ashort-circuit between both the lines at a high frequency, and a primaryradiator disposed in the rotation-side transmission line so as to berotatable together with the rotation-side transmission line forradiating high-frequency signals that have passed through therotation-side transmission line in parallel with the rotation axis ofthe rotation-side transmission line not coaxially with the rotationaxis.

As a result, the fixed-side transmission line is choke-coupled with therotation-side transmission line using the transmission-line side choke,so that high-frequency signals can be propagated through the twotransmission lines. Also, the rotation-side transmission line isprovided with the primary radiator capable of radiating high-frequencysignals in parallel with the rotation axis not coaxially with therotation axis, so that the radiation position of the high-frequencysignal can be moved about the rotation axis as a center by rotating theprimary radiator together with the rotation-side transmission line.

According to a preferred embodiment of the present invention, asecondary radiator is arranged on the line of the radiating direction ofthe primary radiator, and the secondary radiator changes an outgoingradiation direction in accordance with an incident position ofhigh-frequency signals.

As a result, by rotating the primary radiator together with therotation-side transmission line, the incident position of high-frequencysignals can be moved relative to the secondary radiator made of adielectric lens, a bifocal lens, or a parabola reflector so as to changethe outgoing direction of the high-frequency signal emitted from thesecondary radiator. As a result, scanning can be carried out laterallyon a horizontal plane or scanning can be performed in a conical shapewith a beam.

According to a preferred embodiment of the present invention, therespective fixed-side transmission line and the rotation-sidetransmission line preferably include a circular waveguide having apropagation mode in a TM01 mode as the magnetic field distribution thatis axially symmetrical about the propagating direction.

As a result, the fixed-side transmission line or the rotation-sidetransmission line can be easily connected to a rectangular waveguide inthe TE10 mode, for example, so as to easily feed high-frequency signalsto the fixed-side transmission line while the rotation-side transmissionline can be readily connected to the primary radiator such as a hornantenna.

Also, a transmitter/receiver, such as a radar and a communicationapparatus, may be constructed using the antenna apparatus according to apreferred embodiment of the present invention.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an antenna apparatus according to afirst preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view of the antenna apparatusaccording to the first preferred embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of the antenna apparatus viewedin arrow direction III—III of FIG. 1.

FIG. 4 is a cross-sectional view of a rotation-side circular waveguideviewed in arrow direction IV—IV of FIG. 3.

FIG. 5 is a plan view of a fixed-side circular waveguide viewed in arrowdirection V—V of FIG. 3.

FIG. 6 is a characteristic diagram showing the relationship between theinner diameter and the blocking or cut-off frequency of a circularwaveguide.

FIG. 7 is a characteristic diagram showing frequency characteristics ofthe reflection factor and the transmission factor between a rectangularwaveguide and the fixed-side circular waveguide.

FIG. 8 is a characteristic diagram showing frequency characteristics ofthe reflection factor and the transmission factor between the fixed-sidecircular waveguide and the rotation-side circular waveguide.

FIG. 9 is a longitudinal sectional view of an antenna apparatusaccording to a first modification viewed from the same position as thatof FIG. 3.

FIG. 10 is a perspective view of an antenna apparatus according to asecond preferred embodiment of the present invention shown in a state inthat a casing is removed.

FIG. 11 is a longitudinal sectional view of the antenna apparatus viewedin arrow direction XI—XI of FIG. 10.

FIG. 12 is a cross-sectional view of a rotation-side circular waveguideand the casing viewed in arrow direction XII—XII of FIG. 11.

FIG. 13 is a longitudinal sectional view of an antenna apparatusaccording to a third preferred embodiment of the present inventionviewed from the same position as that of FIG. 3.

FIG. 14 is a perspective view of a rotation-side circular waveguideaccording to the third preferred embodiment of the present inventionshown in a single unit.

FIG. 15 is a longitudinal sectional view of an essential portion of therotation-side circular waveguide in FIG. 13.

FIG. 16 is a cross-sectional view of the rotation-side circularwaveguide and the casing viewed in arrow direction XVI—XVI of FIG. 13.

FIG. 17 is a characteristic diagram showing frequency characteristics ofthe reflection factor and the transmission factor between a primaryradiator and the rotation-side circular waveguide.

FIG. 18 is a perspective view of a rotation-side circular waveguideaccording to a second modification shown in a single unit.

FIG. 19 is a perspective view of a rotation-side circular waveguideaccording to a third modification shown in a single unit.

FIG. 20 is a cross-sectional view of a rotation-side circular waveguideand a casing according to a fourth modification at the same position asthat of FIG. 16.

FIG. 21 is a plan view of an antenna apparatus according to a fourthpreferred embodiment of the present invention.

FIG. 22 is a characteristic diagram showing the relationship between thebeam scanning angle and the antenna gain of the antenna apparatus shownin FIG. 21.

FIG. 23 is a sectional view of an antenna apparatus according to a fifthmodification.

FIG. 24 is a plan view of an antenna apparatus according to a sixthmodification.

FIG. 25 is a block diagram of a radar according to a fifth preferredembodiment of the present invention.

FIG. 26 is a block diagram of a radar according to a seventhmodification.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An antenna apparatus and a transmitter/receiver according to a preferredembodiment of the present invention will be described below in detailwith reference to the attached drawings.

First, FIGS. 1 to 8 show the antenna apparatus according to a firstpreferred embodiment and its various frequency characteristics.

In the drawings, reference numeral 1 denotes a fixed-side circularwaveguide as a cylindrical fixed-side transmission line axiallysymmetrical about an axis O, and the fixed-side circular waveguide 1 isprovided with a circular hole 1A perforated with a circular section andextending in an axial direction. The fixed-side circular waveguide 1 hasa propagation mode in a TM01 mode as a magnetic field distribution thatis axially symmetrical (rotationally symmetrical) about a transmissiondirection (axial direction) of high-frequency signals, for example.

The inner diameter φ of the circular hole 1A herein has a value thatallows it to pass through the TM01 mode with a desired frequency in asufficiently low loss state and blocks the next higher-order mode (TE21mode). For example, in blocking or cut-off frequency characteristicsversus the inner diameter φ shown in FIG. 6, when the inner diameter φis less than about 3.5 mm, the TE21 mode with 83 GHz or less can beblocked while when the inner diameter φ is larger than about 3.3 mm, theTM01 mode with 68 GHz or more can be allowed to pass through. Hence, itis understood that when the desired frequency is in a 76 GHz band usedfor an on-vehicle millimeter wave radar, the inner diameter φ ispreferably about 3.4 mm as an intermediate value between about 3.3 mmand about 3.5 mm, for example.

Reference numeral 2 denotes a rectangular waveguide connected to thefixed-side circular waveguide 1, and one end of the rectangularwaveguide 2 is attached to one end (lower end in FIG. 1) of thefixed-side circular waveguide 1 while the other end of the rectangularwaveguide 2 extending outside in a radial direction of a circle withcenter at an axis O. The rectangular waveguide 2 is provided with asubstantially rectangular hole 2A extending in a longitudinal direction(radial direction), and the substantially rectangular hole 2A has asubstantially rectangular section with a height L1 and a width L2. Therectangular waveguide 2 is also provided with a substantiallyrectangular connection hole 2B formed adjacent to the one end at aposition opposing the circular hole 1A of the fixed-side circularwaveguide 1 with a width L2 and a length L3, and the substantiallyrectangular hole 2A and the circular hole 1A are communicated withtogether through the connection hole 2B. Furthermore, around theconnection hole 2B, a back short portion 2C is formed to include aconcavity that is sunken lower than the bottom of the substantiallyrectangular hole 2A by a depth L4 as a space having a distance that islarger than other portions in the axial direction of the fixed-sidecircular waveguide 1.

The rectangular waveguide 2 also has a propagation mode in a TE10 modewith an electric field distribution that is substantially parallel withthe axial direction of the fixed-side circular waveguide 1 and verticaland annular magnetic field distribution, for example. Then, therectangular waveguide 2 is magnetically coupled with the fixed-sidecircular waveguide 1 through the connection hole 2B, so that the TE10mode is converted into the TM01 mode. The portion between the twowaveguides 1 and 2 performs as a mode conversion portion with the backshort portion 2C.

As an example, when the height L1 of the substantially rectangular hole2A is about 1.27 mm; the width L2 is about 2.54 mm; the length L3 of theconnection hole 2B and the back short portion 2C is about 3.4 mm; andthe depth L4 of the back short portion 2C is about 1.0 mm, frequencycharacteristics of the reflection coefficient and the transmissioncoefficient between the rectangular waveguide 2 and the fixed-sidecircular waveguide 1 are shown in FIG. 7. As a result, it is understoodthat high-frequency signals at an approximately 76 GHz band can betransmitted in a low reflected state.

Reference numeral 3 denotes a rotation-side circular waveguide as anaxially symmetrical and cylindrical rotation-side circular waveguide 1,which is provided with a substantially circular hole 3A having acircular cross-section with substantially the same inner diameter φ asthat of the circular hole 1A of the fixed-side circular waveguide 1 andextending in an axial direction, and the substantially circular hole 3Aextends to a halfway position in the axial direction. The rotation-sidecircular waveguide 3 is spaced from the fixed-side circular waveguide 1by a space δ1 while being coaxially arranged along the axis O of thefixed-side circular waveguide 1 and is rotatable about the axis O alongthe entire circumference using a motor 7, which will be described later.

One end (lower end in FIG. 1) of the rotation-side circular waveguide 3opposes the other end of the fixed-side circular waveguide 1 such thatthe substantially circular hole 3A opposes the circular hole 1A. On theother hand, the other end (upper end in FIG. 1) of the rotation-sidecircular waveguide 3 is closed with a substantially circular disc-likelid 3B while being attached in a state having a primary radiator 5 builttherein, which will be described later.

The rotation-side circular waveguide 3 herein has a propagation mode ina TM01 mode with magnetic field distribution that is axially symmetrical(rotationally symmetrical) about the transmission direction (axialdirection) of high-frequency signals, for example, as the samepropagation mode as that of the fixed-side circular waveguide 1. Then,the rotation-side circular waveguide 3 is magnetically coupled with thefixed-side circular waveguide 1 so that the high-frequency signals inthe TM01 mode are transmitted therethrough.

Reference numeral 4 denotes a waveguide-side choke provided in thefixed-side circular waveguide 1 at a position between the fixed-sidecircular waveguide 1 and the rotation-side circular waveguide 3 as atransmission line-side choke. The waveguide-side choke 4 includes asubstantially ring-shaped circular groove. The waveguide-side choke 4 isalso spaced from the outermost periphery of the circular hole 1A by aspace L5.

Furthermore, the waveguide-side choke 4 having a width L6 and a depth L7is concavely formed on an open end surface of the fixed-side circularwaveguide 1 opposing the rotation-side circular waveguide 3. Thereby,the waveguide-side choke 4 virtually shorts portions (portion “a” inFIG. 3) in the vicinity of the outermost peripheries of the circularholes 1A and 3A of the circular waveguides 1 and 3.

As an example, when the space δ1 between the circular waveguides 1 and 3is about 0.15 mm; the space L5 is about 0.5 mm; the width L6 of thewaveguide-side choke 4 is about 1.0 mm; and the depth L7 thereof isabout 1.5 mm, frequency characteristics of the reflection coefficientand the transmission coefficient between the circular waveguides 1 and 3are shown in FIG. 8. As a result, it is understood that high-frequencysignals at an approximately 76 GHz band can be transmitted in a lowreflected state.

Reference numeral 5 denotes a primary radiator attached to therotation-side circular waveguide 3 in a built-in state. The primaryradiator 5 having a substantially rectangular section, for example,includes a waveguide horn antenna that is arranged to gradually expandradially to the outside. The end extremity of the primary radiator 5herein is opened on the side surface of the rotation-side circularwaveguide 3. Thereby, the primary radiator 5 can radiate ahigh-frequency signal beam in a direction that is substantiallyperpendicular to the axis O, for example, as a direction that isdifferent from the rotational axis (axis O). On the other hand, the baseend of the primary radiator 5 is connected to a rectangular waveguideportion 6 including a substantially rectangular hole radially extendingwith a substantially rectangular section.

The rectangular waveguide portion 6 is provided with a substantiallyrectangular connection hole 6A formed at a position opposing thesubstantially circular hole 3A of the rotation-side circular waveguide3, and having a shape similar to the substantially rectangular hole 2Aof the rectangular waveguide 2, for example, and extending to the otherend (upper end in FIG. 1) of the substantially circular hole 3A of therotation-side circular waveguide 3. The rectangular waveguide portion 6is communicated with the substantially circular hole 3A through theconnection hole 6A. Furthermore, around the connection hole 6A, there isprovided a back short portion 6B with a space larger than other portionsin the axial direction of 3 so as to have a shape similar to the backshort portion 2C, for example.

The rectangular waveguide portion 6 has a propagation mode in a TM01mode, for example, and is magnetically coupled with the rotation-sidecircular waveguide 3 through the connection hole 2B while a matchedstate is maintained between the rectangular waveguide portion 6 and therotation-side circular waveguide 3 by the back short portion 6B.

Reference numeral 7 denotes a motor attached to the lid 3B of therotation-side circular waveguide 3. The motor 7, together with thefixed-side circular waveguide 1 for example, is fixed to a casing (notshown), etc., so as to continuously rotate the rotation-side circularwaveguide 3 about the axis O in all directions.

The waveguide according to the present preferred embodiment preferablyhas the unique configuration described above. The operation of thepresent preferred embodiment will now be described.

First, upon inputting high-frequency signals, such as millimeter waves,into the rectangular waveguide 2, the high-frequency signals arepropagated through the rectangular waveguide 2 in the TE10 mode so as toreach the connection hole 2B. At this time, the rectangular waveguide 2is coupled with the fixed-side circular waveguide 1 through theconnection hole 2B, so that the high-frequency signals are convertedinto the TM01 mode from the TE10 mode, and are propagated through thefixed-side circular waveguide 1. Since the fixed-side circular waveguide1 is arranged coaxially with the rotation-side circular waveguide 3, thehigh-frequency signals in the axially symmetrical TM01 mode arepropagated through the rotation-side circular waveguide 3 regardless ofthe rotational displacement of the rotation-side circular waveguide 3.Also, since the rotation-side circular waveguide 3 is connected to theprimary radiator 5 via the rectangular waveguide portion 6, thehigh-frequency signals are radiated outside from the primary radiator 5.

Still, according to the present preferred embodiment, the fixed-sidecircular waveguide 1 is arranged coaxially with the rotation-sidecircular waveguide 3, and both the waveguides have an axiallysymmetrical propagation mode in the TM01 mode, so that high-frequencysignals can be propagated through the fixed-side circular waveguide 1and the rotation-side circular waveguide 3 regardless of the rotationaldisplacement of the rotation-side circular waveguide 3.

Between the fixed-side circular waveguide 1 and the rotation-sidecircular waveguide 3, the waveguide-side choke 4 is provided, so thatboth the waveguides are choke-coupled together and short-circuited at ahigh-frequency using the waveguide-side choke 4 so as to prevent thehigh-frequency signal from leaking from the gap between both thewaveguides.

Furthermore, since the rotation-side circular waveguide 3 is providedwith the primary radiator 5 that can radiate a high-frequency signal ina direction that is different from the rotational axis, thehigh-frequency signal can be radiated using the primary radiator 5 in adirection that is substantially perpendicular to the propagationdirection of the rotation-side circular waveguide 3. Because the primaryradiator 5 is constructed to rotate in conjunction with therotation-side circular waveguide 3, while the whole circumference can bescanned with high-frequency signals about the rotational axis, thehigh-frequency signal can be radiated over an arbitrary angular rangethrough the primary radiator by blocking an unnecessary radiation range,such as a semicircle, using a casing as long as the range is within 360°(whole circumference).

Also, when the antenna apparatus according to the present preferredembodiment is applied to a radar, while wide angle detection is possibleover the whole circumference, angular resolution is greatly improvedbecause of the detection at an arbitrary angle.

Furthermore, according to the present preferred embodiment, therotation-side circular waveguide 3 is rotated in a predetermineddirection (constant-speed rotation) using the motor 7, so that theconstant-acceleration rotation, such as reciprocal movement, is notnecessary unlike in a conventional technique so as to reduce themechanical load to the driving system (the motor 7), thereby improvingreliability and durability.

Also, the entire antenna apparatus has a simplified structure includingthe two circular waveguides 1 and 3 so as to be easily manufactured bycutting and injection molding, thereby reducing manufacturing cost.

Furthermore, since the circular waveguides 1 and 3 having a propagationmode in the TM01 mode are used, the fixed-side circular waveguide 1 orthe rotation-side circular waveguide 3 can be easily connected to therectangular waveguide 2 in the TE10 mode, for example, so as to easilyfeed high-frequency signals to the fixed-side circular waveguide 1 whilethe rotation-side circular waveguide 3 can be readily connected to theprimary radiator 5 such as a horn antenna.

In addition, according to the first preferred embodiment, high-frequencysignals are preferably propagated through the circular waveguides 1 and3 in the TM01 mode. However, any high-frequency signals in a mode inwhich electric field distribution or magnetic field distribution isaxially symmetrical, may be propagated, so that high-frequency signalsin other modes, such as the TE01 mode and a coaxial TEM mode, may alsobe propagated.

Also, according to the first preferred embodiment, the waveguide-sidechoke is preferably constructed of the waveguide-side choke 4 includingthe ring-shaped groove surrounding the circular hole 1A. However, thepresent invention is not limited to this construction and thewaveguide-side choke may also be constructed of any choke composed of apolygonal groove, such as a triangular or square groove, as long as thegroove surrounds the circular hole.

According to the first preferred embodiment, the waveguide-side choke 4is arranged on the opened end surface of the fixed-side circularwaveguide 1. Alternatively, the waveguide-side choke may be arranged onthe opened end surface of the rotation-side circular waveguide 3, or thewaveguide-side chokes may also be provided on both the circularwaveguides 1 and 3.

According to the first preferred embodiment, the primary radiator 5preferably radiates a high-frequency signal beam in a direction that issubstantially perpendicular to the rotational axis (the axis O) of therotation-side circular waveguide 3. However, the present invention isnot limited to this, so that if the high-frequency signal beam can beoutside radiated radially from the rotational axis, the high-frequencysignal beam may also be radiated in a direction inclined by an angle arelative to the rotational axis, as shown in FIG. 3, by attaching theprimary radiator to be inclined.

According to the first preferred embodiment, the primary radiator 5preferably includes the waveguide horn antenna with a substantiallyrectangular section. However, the present invention is not limited tothis and the primary radiator may have other sections, such as asubstantially circular or substantially elliptical section, so as toappropriately establish antenna characteristics, such as an antennagain, a sidelobe level, and a beam width, responding to various demands.Moreover, the primary radiator is not limited to the waveguide hornantenna, so that other antenna devices, such as a microstrip antenna,may also be used.

Also, according to the first preferred embodiment, the rotation-sidecircular waveguide 3 and the primary radiator 5 are preferably connectedtogether via the rectangular waveguide portion 6. However, the presentinvention is not limited to this, so that a primary radiator 8 may alsobe directly connected to a portion of a circular hole 3A′ like in afirst modification shown in FIG. 9.

Moreover, according to the first preferred embodiment, the primaryradiator 5 is preferably attached to the rotation-side circularwaveguide 3 in a built-in state. Alternatively, the primary radiator 5may be attached to the side surface of the rotation-side circularwaveguide 3 to protrude therefrom by extending the rectangular waveguideportion 6 to the side surface (external periphery) of the rotation-sidecircular waveguide 3.

Next, FIGS. 10 to 12 show an antenna apparatus according to a secondpreferred embodiment of the present invention. One of the uniquefeatures of the present preferred embodiment is that a rotation-sidecircular waveguide is provided with two primary radiators attachedthereto. In addition, according to the present preferred embodiment,like reference characters designate like components common to the firstpreferred embodiment and the description thereof is omitted.

Reference numeral 11 denotes a rotation-side circular waveguideaccording to the second preferred embodiment. The rotation-side circularwaveguide 11 preferably has an axially symmetrical and cylindrical shapesimilar to the rotation-side circular waveguide 3 according to the firstpreferred embodiment. Also, the rotation-side circular waveguide 11 isprovided with a substantially circular hole 11A perforated with asubstantially circular section with substantially the same innerdiameter as the circular hole 1A of the fixed-side circular waveguide 1and extending in an axial direction. The substantially circular hole 11Aextends to a halfway position in the axial direction, so thathigh-frequency signals can be propagated in the TM01 mode.

The rotation-side circular waveguide 11 is spaced from the fixed-sidecircular waveguide 1 by a space of about 0.15 mm while being arrangedcoaxially with the axis O of the fixed-side circular waveguide 1 and isrotatable over the whole circumference about the axis O by a motor 16,which will be described later.

One end (lower end in FIG. 10) of the rotation-side circular waveguide11 opposes the other end of the fixed-side circular waveguide 1, and theother end (upper end in FIG. 10) of the rotation-side circular waveguide11 is closed with a disc-like lid 11B. The rotation-side circularwaveguide 11 is magnetically coupled with the fixed-side circularwaveguide 1 and high-frequency signals are propagated between thewaveguides in the TM01 mode.

Reference numeral 12 denotes two primary radiators attached to therotation-side circular waveguide 11 in a built-in state. Each primaryradiator 12 preferably includes a waveguide horn antenna in a mannersimilar to the primary radiator 5 according to the first preferredembodiment. The two primary radiators 12 are radially arranged indirections that are different from each other from the rotational axis(the axis O) as a center, opposite to each other, for example. The endextremity of the primary radiator 12 is opened on the side surface ofthe rotation-side circular waveguide 11. On the other hand, the base endof the primary radiator 12 radially extends to be connected to arectangular waveguide portion 13 with a propagation mode in the TE10mode.

The rectangular waveguide portion 13 is provided with a substantiallyrectangular connection hole 13A formed at a position opposing thesubstantially circular hole 11A of the rotation-side circular waveguide11 and extending to the other end (upper end in FIG. 10) of thesubstantially circular hole 11A of the rotation-side circular waveguide11. Furthermore, around the connection hole 13A, a back short portion13B is formed to have a space distance larger than other portions in theaxial direction of the rotation-side circular waveguide 11.

Reference numeral 14 denotes a casing arranged to surround the circularwaveguides 1 and 11, and the casing 14 includes a cylinder portion 14Afixed to the fixed-side circular waveguide 1 and the rectangularwaveguide 2 so as to cover the external periphery of the rotation-sidecircular waveguide 11, and a top board portion 14B arranged at the upperend of the cylinder portion 14A so as to cover the lid 11B of therotation-side circular waveguide 11. The cylinder portion 14A isprovided with an accommodation hole 14C formed inside so as toaccommodate the rotation-side circular waveguide 11 therein to have agap δ2 of about 0.15 mm relative to the external surface of therotation-side circular waveguide 11.

Reference numeral 15 denotes a radiator opening formed in the cylinderportion 14A, and the radiator opening 15, as shown in FIG. 12, ispenetrated at a position (opposable position) corresponding to theprimary radiator 12. The radiator opening 15 has an area that is greaterthan that of the opening of the primary radiator 12, and is opened overan angular range β about the rotational axis (the axis O) of therotation-side circular waveguide 11. The radiator opening 15 isconnected to the two primary radiators 12 rotating together with therotation-side circular waveguide 11 sequentially from any one of the tworadiators.

Reference numeral 16 denotes a motor fixed to the top board portion 14Bof the casing 14. The rotational axis of the motor 16 is attached to thelid 11B of the rotation-side circular waveguide 11 so as to continuouslyrotate the rotation-side circular waveguide 11 about the axis O in alldirections by the motor 16.

In such a manner, according to the present preferred embodiment, thesame effects and advantages as those achieved by the first preferredembodiment can also be obtained. Moreover, according to the presentpreferred embodiment, while the two primary radiators 12 arranged indirections opposite to each other are provided in the rotation-sidecircular waveguide 11, the respective primary radiators 12 aresequentially connected to the radiator opening 15 of the casing 14 alongwith the rotation of the rotation-side circular waveguide 11, so thatwhile one of the primary radiators 12 is radiating high-frequencysignals, the other is surrounded by the casing 14 so that the radiationof the high-frequency signals can be blocked. Thereby, while therotation-side circular waveguide 11 is making one revolution, the twoprimary radiators 12 are connected to the radiator opening 15 so as toradiate the high-frequency signals, so that in comparison with thesingle primary radiator attached thereto, a period of time radiating thehigh-frequency signals in a predetermined direction through the radiatoropening 15 within one revolution can be increased so as to increase thedetection period and communication period.

In particular, when the angle β of the radiator opening 15 is 180°, anyone of the two primary radiators 12 arranged in directions opposite toeach other across the rotational axis as the center is always connectedto the radiator opening 15, so that detection or communication can bealways carried out.

According to the present preferred embodiment, the two primary radiators12 are preferably attached to the rotation-side circular waveguide 11.Alternatively, three or more primary radiators may be attached. While aplurality of primary radiators are arranged at equal intervals (120°intervals when three radiators are provided, for example) in thecircumferential direction about the rotational axis of the rotation-sidecircular waveguide as the center, in accordance with the intervals, theangular range (120° intervals when three radiators are provided, forexample) of the radiator opening of the casing may be established. Also,a plurality of primary radiators may be arranged at different intervalsin the circumferential direction about the rotational axis of therotation-side circular waveguide as the center.

Furthermore, according to the present preferred embodiment, the twoprimary radiators 12 are preferably radially arranged about therotational axis of the rotation-side circular waveguide 11 as thecenter. However, they may be arranged in different directions from eachother, and they may be spirally arranged, for example.

Next, FIGS. 13 to 17 show an antenna apparatus and frequencycharacteristics regarding the antenna apparatus according to a thirdpreferred embodiment of the present invention. One of the uniquefeatures of the third preferred embodiment is that while a rotation-sidecircular waveguide is provided with two primary radiators attachedthereto, a radiator-side choke is provided around an open end of eachprimary radiator. In addition, according to the present preferredembodiment, like reference characters designate like components commonto the first preferred embodiment and the description thereof isomitted.

Reference numeral 21 denotes a rotation-side circular waveguideaccording to the third preferred embodiment. The rotation-side circularwaveguide 21 preferably has an axially symmetrical and cylindrical shapesimilar to the rotation-side circular waveguide 3 according to the firstpreferred embodiment. Also, the rotation-side circular waveguide 21 isprovided with a substantially circular hole 21A perforated with asubstantially circular section with substantially the same innerdiameter as the circular hole 1A of the fixed-side circular waveguide 1and extending in an axial direction. The substantially circular hole 21Aextends to a halfway position in the axial direction.

The rotation-side circular waveguide 21 is spaced from the fixed-sidecircular waveguide 1 by a space of about 0.15 mm while being arrangedcoaxially with the axis O of the fixed-side circular waveguide 1 and isrotatable about the axis O. One end of the rotation-side circularwaveguide 21 has the substantially circular hole 21A opened therefrom,and the other end of the rotation-side circular waveguide 21 is closedwith a disc-like lid 21B. Furthermore, the rotation-side circularwaveguide 21 is surrounded with a casing 25, which will be describedlater, and spaced from the casing 25 by a space δ2. The rotation-sidecircular waveguide 21 is magnetically coupled with the fixed-sidecircular waveguide 1 and high-frequency signals are propagated betweenthe waveguides in the TM01 mode.

Reference numeral 22 denotes two primary radiators attached to therotation-side circular waveguide 21 in a built-in state. Each primaryradiator 22 preferably includes a waveguide horn antenna graduallyexpanding at an expanding angle φ in a manner similar to the primaryradiator 5 according to the first preferred embodiment. The two primaryradiators 22 are radially arranged in directions that are different fromeach other from the rotational axis (the axis O) as a center at equalintervals in the circumferential direction (directions opposite to eachother). The end extremity of each primary radiator 22 is opened on theside surface of the rotation-side circular waveguide 21. On the otherhand, the base end of the primary radiator 22 radially extends to beconnected to a rectangular waveguide portion 23 with a propagation modein the TE10 mode.

The rectangular waveguide portion 23 is provided with a substantiallyrectangular connection hole 23A formed at a position opposing thesubstantially circular hole 21A of the rotation-side circular waveguide21 so as to have substantially the same size as that of thesubstantially rectangular hole 2A of the rectangular waveguide 2according to the first preferred embodiment and to extend to the otherend of the substantially circular hole 21A of the rotation-side circularwaveguide 21. Furthermore, around the connection hole 23A, a back shortportion 23B is formed for matching the rotation-side circular waveguide21 (the substantially circular hole 21A) with the rectangular waveguideportion 23.

Reference numeral 24 denotes a radiator-side choke provided in therotation-side circular waveguide 21 to surround the open end of theprimary radiator 22, and two radiator-side chokes 24 are provided on theexternal surface of the rotation-side circular waveguide 21corresponding to the two respective primary radiators 22, and includesubstantially elliptical (substantially rectangular) grooves. Also, theradiator-side choke 24 is arranged at a position spaced from the centerof the open end of the primary radiator 22 by a space L8.

Furthermore, the radiator-side choke 24 has a width L9 and a depth L10,and is concavely arranged on the external surface of the rotation-sidecircular waveguide 21. Thereby, the radiator-side choke 24 virtuallyshorts between the vicinity of the open end of the primary radiator 22and the casing 25 which will be described later.

As an example, when one primary radiator 22 is opposed (blocked) to thecasing 25 and the other is opened (capable of radiating), frequencycharacteristics of the reflection factor and the transmission factorbetween the other primary radiator 22 and the rotation-side circularwaveguide 21 are shown in FIG. 17. Where the expanding angle φ of theprimary radiator 22 is 0°; the space δ2 between the rotation-sidecircular waveguide 21 and the casing 25 is about 0.15 mm; the space L8is about 1.7 mm; the width L9 of the radiator-side choke 24 is about 1.0mm; the depth L10 is about 1.2 mm; the distance L11 from the rotationalaxis to the open end of the primary radiator 22 is about 4.5 mm; thelength L12 of the back short portion 23B is about 3.4 mm; and the heightL13 of the back short portion 23B is about 0.8 mm. As a result, it isunderstood that high-frequency signals at an approximately 76 GHz bandcan be transmitted in a low reflection state.

Reference numeral 25 denotes a casing arranged to surround the circularwaveguides 1 and 21, and the casing 25 preferably includes a cylinderportion 25A fixed to the fixed-side circular waveguide 1 and therectangular waveguide 2 so as to cover the external periphery of therotation-side circular waveguide 21, and a top board portion 25Barranged at the upper end of the cylinder portion 25A so as to cover thelid 21B of the rotation-side circular waveguide 21. The cylinder portion25A is provided with an accommodation hole 25C formed inside so as toaccommodate the rotation-side circular waveguide 21 therein.

Reference numeral 26 denotes a radiator opening formed in the cylinderportion 25A, and the radiator opening 26, as shown in FIG. 16, ispenetrated at a position (opposable position) corresponding to theprimary radiator 22. The radiator opening 26 has an area greater thanthat of the opening of the primary radiator 22, and is opened over apredetermined angular range about the rotational axis (the axis O) ofthe rotation-side circular waveguide 21. The radiator opening 26 isconnected to the two primary radiators 22 rotating together with therotation-side circular waveguide 21 sequentially from any one of the tworadiators.

Reference numeral 27 denotes a motor fixed to the top board portion 25Bof the casing 25. The rotational axis of the motor 27 is attached to thelid 21B of the rotation-side circular waveguide 21 so as to continuouslyrotate the rotation-side circular waveguide 21 about the axis O in alldirections by the motor 27.

In such a manner, according to the present preferred embodiment, thesame effects and advantages as those achieved by the first and thesecond preferred embodiments can also be obtained. Moreover, accordingto the present preferred embodiment, while the two primary radiators 22arranged in directions opposite to each other are preferably provided inthe rotation-side circular waveguide 21, the respective primaryradiators 22 are sequentially connected to the radiator opening 26 ofthe casing 25 along with the rotation of the rotation-side circularwaveguide 21, so that while one of the primary radiators 22 is radiatinghigh-frequency signals, the other is surrounded by the casing 25 so thatthe radiation of the high-frequency signals can be blocked.

Since the radiator-side choke 24 is provided on the external surface ofthe rotation-side circular waveguide 21 so as to surround the open endof the primary radiator 22 especially according to the present preferredembodiment, the open end of one of the two primary radiators 22, whichis surrounded with the casing 25, and the casing 25 can be shorted at ahigh-frequency using the radiator-side choke 24. As a result, while oneof the primary radiators 22 is radiating high-frequency signals throughthe radiator opening 26, the high-frequency signals can be preventedfrom leaking through between the residual primary radiator 22 and thecasing 25, so that the loss of the entire antenna apparatus can beprevented.

According to the third preferred embodiment, the radiator-side chokes 24are preferably provided on the external surface of the rotation-sidecircular waveguide 21 so as to surround the open end of the respectiveprimary radiators 22. However, the present invention is not limited tothis, so that two ring-shaped concave grooves 31A may also be formed toconstitute radiator-side chokes 31 on the external surface of therotation-side circular waveguide 21 above and below the two primaryradiators 22 (on both sides in the axial direction) as in a secondmodification shown in FIG. 18.

As in a third modification shown in FIG. 19, two first ring-shapedconcave grooves 32A may be formed on the external surface of therotation-side circular waveguide 21 above and below the two primaryradiators 22 (on both sides in the axial direction) while secondstraight concave grooves 32B intersecting with the first concave grooves32A may be formed on the right and left of the primary radiators 22 (onboth sides in the circumferential direction) so as to constituteradiator-side chokes 32 of the first and second concave grooves 32A and32B. In this case, the protrusion length L14 of the second concavegroove 32B from the first concave groove 32A may be about λ/4 (L14≈λ/4),where λ is the wavelength under vacuum at used frequency band.

Moreover, according to the third preferred embodiment, the radiator-sidechokes 24 are preferably provided on the external surface of thecylindrical rotation-side circular waveguide 21. However, the presentinvention is not limited to this, so that as in a fourth modificationshown in FIG. 20, on one surface of a rotation-side circular waveguide21′ with a substantial cubic external shape, a primary radiator 22′ maybe opened while a radiator-side choke 24′ may be formed on the samesurface as the one on which the primary radiator 22′ is opened. In thiscase, a casing 25′ has an accommodation hole 25C′ within which therotation-side circular waveguide 21′ having a substantially squaresection is rotatable. Thereby, the radiator-side choke 24′ can be shapedon a plane so that fabrication of the radiator-side choke 24′ isfacilitated.

According to the third preferred embodiment, the radiator-side chokes 24are preferably provided on the external surface of the rotation-sidecircular waveguide 21. Alternatively, they may be formed on theaccommodation hole 25C of the casing 25 or may be formed on both therotation-side circular waveguide 21 and the casing 25.

Next, FIG. 21 shows an antenna apparatus according to a fourth preferredembodiment of the present invention. One of the unique features of thefourth preferred embodiment is that in the radiating direction of theprimary radiator, a secondary radiator is provided, which can change theradiating direction in accordance with the incident position ofhigh-frequency signals. In addition, according to the present preferredembodiment, like reference characters designate like components commonto the first preferred embodiment and the description thereof isomitted.

Reference numeral 41 denotes a secondary radiator made of a dielectriclens with a diameter φ1 and a thickness T arranged on the line of theradiating direction of the primary radiator 5. The secondary radiator 41is fixed in a state spaced from the rotation-side circular waveguide 3by a distance L15.

As an example, when the rotation-side circular waveguide 3 is rotated bya rotation angle θ1, the relationship between the scanning angle θ2 ofthe beam radiated from the secondary radiator 41 and the antenna gain isinvestigated. The results are shown in FIG. 22. Where, the diameter φ1of the secondary radiator 41 is about 90 mm; the thickness T is about 18mm; and the distance L15 is about 27 mm. The rotation angle θ1 ischanged from 0° to 60°, as it is 0° when the primary radiator 5approaches (faces) the secondary radiator 41 at most. As a result, whenthe rotation angle θ1 is changed in a range of −30° to +30° (θ1=−30° to+30°), the beam scanning angle θ2 can be changed from −10° to +10°(θ2=−10° to +10°) with the antenna gain obtained sufficiently, so thatthe apparatus is understood to be applicable to an ACC (adaptive cruisecontrol) radar.

In such a manner, according to the present preferred embodiment, thesame effects and advantages as those achieved by the first preferredembodiment can also be obtained. Moreover, since the secondary radiator41 is provided on the line of the radiating direction, the incidentposition of high-frequency signals can be moved relative to thesecondary radiator 41 by rotating the primary radiator 5 with therotation-side circular waveguide 3 together so as to change an outgoingdirection of the high-frequency signals emitted from the secondaryradiator 41. As a result, scanning can be carried out laterally on ahorizontal plane with the high-frequency signals, so that the apparatuscan be applied to an ACC radar.

In addition, according to the fourth preferred embodiment, thedielectric lens is preferably used as the secondary radiator 41.Alternatively, as in a fifth modification shown in FIG. 23, a parabolareflector may be used as a secondary radiator 41′. In this case, whenthe radiating direction of a primary radiator 5′ is inclined about therotation axis of the rotation-side circular waveguide 3 by an angle α(α=10° to 80°, for example), the high-frequency signals can be rathereasily entered into the secondary radiator 41′.

Furthermore, according to the fourth preferred embodiment, the primaryradiator 5 is preferably arranged in a direction that is different fromthat of the rotation axis of the rotation-side circular waveguide 3.Alternatively, as in a sixth modification shown in FIG. 24, a primaryradiator 5″ that is arranged in parallel with the rotation axis and notcoaxially with the rotation axis may be used. In this case, by thesecondary radiator, scanning can be performed with a beam, and when asecondary radiator 41″ including a bifocal lens is used, scanning can beperformed in a conical shape with a beam.

Next, FIG. 25 shows a fifth preferred embodiment of the presentinvention. One of the unique features of the fifth preferred embodimentis that using the antenna apparatus according to various preferredembodiments of the present invention, a radar is constructed as atransmitter/receiver.

Reference numeral 51 denotes a radar, and the radar 51 preferablyincludes a voltage-controlled oscillator 52, an antenna apparatus 55according to any of the first to fourth preferred embodiments andconnected to the voltage-controlled oscillator 52 via an amplifier 53and a circulator 54, and a mixer 56 connected to the circulator 54 fordown-converting the signals received from the antenna apparatus 55 intointermediate-frequency signals IF. Between the amplifier 53 and thecirculator 54, a directional coupler 57 is connected, and by thedirectional coupler 57, power-distributed signals are transmitted to themixer 56 as local signals.

The radar according to the present preferred embodiment has the uniquestructure described above, and the oscillatory signal produced from thevoltage-controlled oscillator 52 is amplified by the amplifier 53 andsent from the antenna apparatus 55 via the directional coupler 57 andthe circulator 54 as a sending signal. On the other hand, the signalreceived from the antenna apparatus 55 is transmitted to the mixer 56via the circulator 54 while being down-converted using the local signalfrom the directional coupler 57 so as to be produced as theintermediate-frequency signal IF.

In such a manner, according to the present preferred embodiment, sincethe radar is constructed using the antenna apparatus 55, by rotating theprimary radiator of the antenna apparatus 55, high-frequency signals canbe sent or received in all directions.

In addition, according to the fifth preferred embodiment, the antennaapparatus 55 preferably has a structure sharing transmitting withreceiving. Alternatively, like in a seventh modification shown in FIG.26, a structure having a transmitting antenna apparatus 61 that isseparate from a receiving antenna apparatus 62 may also be used.

According to the fifth preferred embodiment described above, the radarincorporates the antenna apparatus according to any of various preferredembodiments of the present invention. Alternatively, the antennaapparatus may be applied to a communication apparatus as atransmitter/receiver.

As is described in detail above, according to preferred embodiments ofthe present invention, the fixed-side transmission line is arrangedcoaxially with the rotation-side transmission line and both the lineshave an axially symmetrical electric field distribution or magneticfield distribution, so that high-frequency signals in the same mode canbe propagated through the fixed-side transmission line and therotation-side transmission line regardless of the rotationaldisplacement of the rotation-side transmission line. Between thefixed-side transmission line and the rotation-side transmission line,the transmission-line side choke is provided, so that both the lines canbe choke-coupled together and short-circuited at a high-frequency usingthe transmission-line side choke so as to prevent the high-frequencysignal from leaking from the gap between both the lines. Furthermore,the rotation-side transmission line is provided with the primaryradiator radiating high-frequency signals in a direction different fromthe rotation axis, so that using the primary radiator, thehigh-frequency signal can be radiated in a direction such as aperpendicular direction and a direction inclined by a predeterminedangle relative to the radiating direction of the rotation-sidetransmission line.

Since the primary radiator is constructed to rotate with therotation-side transmission line together, while wide angle detection andhigh angular resolution can be achieved, the entire antenna apparatusstructure is simplified, thereby reducing manufacturing cost. Since theprimary radiator can be driven at a constant speed in a predetermineddirection together with the rotation-side transmission line, the load ofthe primary radiator to the driving system can be reduced, therebyimproving reliability and durability.

If a plurality of the primary radiators are provided in therotation-side transmission line, and the plurality of the primaryradiators are arranged to direct themselves in directions that aredifferent from each other, when any primary radiators directed in apredetermined direction in the plurality of the rotating primaryradiators are enabled to radiate signals while the residual primaryradiators are blocked, in comparison with the single primary radiatorattached thereto, a period of time of radiating the high-frequencysignals in the predetermined direction within one revolution can beincreased so as to increase the detection period and communicationperiod.

Furthermore, when a casing is arranged around the plurality of theprimary radiators for surrounding the primary radiators, and the casingis provided with a radiator opening formed thereon, to which any one ofthe plurality of rotating primary radiators is sequentially connected,in comparison with the single primary radiator attached thereto, aperiod of time of radiating the high-frequency signals through theradiator opening within one revolution of the rotation-side transmissionline can be increased so as to increase the detection period andcommunication period.

Moreover, when a radiator-side choke is provided between the pluralityof primary radiators and the casing, while one primary radiator isradiating high-frequency signals through the radiator opening, thehigh-frequency signals can be prevented from leaking through between theresidual primary radiators and the casing, so that the loss of theentire antenna apparatus can be minimized.

Furthermore, when the rotation-side transmission line is provided withthe primary radiator that is capable of radiating high-frequency signalsin parallel with the rotation axis not coaxially with the rotation axis,the radiation position of the high-frequency signal can be moved aboutthe rotation axis as a center by rotating the primary radiator togetherwith the rotation-side transmission line. Thereby, by arranging thesecondary radiator on the line of the radiating direction of the primaryradiator, scanning can be carried out with a high-frequency signal beam,so that the antenna apparatus can be applied to an ACC radar.

Furthermore, when a secondary radiator, which changes an outgoingradiation direction in accordance with an incident position ofhigh-frequency signals, is arranged on the line of the radiatingdirection of the primary radiator, by rotating the primary radiatortogether with the rotation-side transmission line, the incident positionof high-frequency signals can be moved relative to the secondaryradiator so as to change the outgoing direction of the high-frequencysignal emitted from the secondary radiator. As a result, scanning can becarried out laterally on a horizontal plane or scanning can be performedin a conical shape with a beam.

Moreover, when the respective fixed-side transmission line and therotation-side transmission line are made of a circular waveguide havinga propagation mode in a TM01 mode, the fixed-side transmission line orthe rotation-side transmission line can be easily connected to arectangular waveguide in a TE10 mode, for example, so as to easily feedhigh-frequency signals to the fixed-side transmission line while therotation-side transmission line can be readily connected to the primaryradiator such as a horn antenna.

Furthermore, when a transmitter/receiver is constructed using theantenna apparatus according to various preferred embodiments of thepresent invention, the entire antenna apparatus structure is simplifiedso as to reduce manufacturing cost while the load to a driving systemfor the primary radiator is reduced, thereby improving reliability anddurability.

As described above, in the antenna apparatus according to preferredembodiments of the present invention, while wide angle detection andhigh angular resolution can be achieved, the entire antenna apparatusstructure is simplified so as to reduce manufacturing cost. Thus, theapparatus is suitable for use as a radar, for example, for scanning withhigh-frequency electromagnetic waves (high-frequency signals), such asmicro waves and millimeter waves, over a predetermined angular range.

While the present invention has been described with respect to preferredembodiments, it will be apparent to those skilled in the art that thedisclosed invention may be modified in numerous ways and may assume manyembodiments other than those specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention which fall within the true spirit andscope of the invention.

1. An antenna apparatus comprising: a fixed-side transmission linehaving an electric field distribution or a magnetic field distributionthat is axially symmetrical in a propagating direction; a rotation-sidetransmission line, having an axially symmetrical electric fielddistribution or magnetic field distribution, arranged coaxially with thefixed-side transmission line so as to be rotatable about an axis of thefixed-side transmission line; a transmission-line side choke disposedbetween the fixed-side transmission line and the rotation-sidetransmission line and arranged to cause a short-circuit between thefixed-side transmission line and the rotation-side transmission line ata high frequency; and a primary radiator disposed in the rotation-sidetransmission line so as to be rotatable together with the rotation-sidetransmission line for radiating high-frequency signals that have passedthrough the rotation-side transmission line in a direction that isdifferent from that of a rotation axis of the rotation-side transmissionline.
 2. The apparatus according to claim 1, wherein a plurality of theprimary radiators are provided in the rotation-side transmission line,and the plurality of the primary radiators are arranged to directthemselves in directions that are different from each other.
 3. Theapparatus according to claim 2, further comprising a casing arrangedaround the plurality of the primary radiators so as to surround theplurality of primary radiators, wherein the casing includes a radiatoropening formed thereon and arranged such that any one of the pluralityof rotating primary radiators can be sequentially connected to theradiator opening.
 4. The apparatus according to claim 3, furthercomprising a radiator-side choke disposed between the plurality ofprimary radiators and the casing, wherein when one of the primaryradiators is connected to the radiator opening, the other primaryradiators and the casing are shorted therebetween by the radiator-sidechoke at high frequency.
 5. The apparatus according to claim 1, furthercomprising a secondary radiator arranged on the line of the radiatingdirection of the primary radiator, the secondary radiator changing anoutgoing radiation direction in accordance with an incident position ofhigh-frequency signals.
 6. The apparatus according to claim 5, whereineach of the fixed-side transmission line and the rotation-sidetransmission line includes a circular waveguide having a propagationmode in a TM01 mode as the magnetic field distribution that is axiallysymmetrical about the propagating direction.
 7. A transmitter/receiverincluding the antenna apparatus according to claim
 6. 8. Atransmitter/receiver including the antenna apparatus according to claim5.
 9. The apparatus according to claim 1, wherein each of the fixed-sidetransmission line and the rotation-side transmission line includes acircular waveguide having a propagation mode in a TM01 mode as themagnetic field distribution that is axially symmetrical about thepropagating direction.
 10. A transmitter/receiver including the antennaapparatus according to claim
 1. 11. An antenna apparatus comprising: afixed-side transmission line having an electric field distribution or amagnetic field distribution that is axially symmetrical in a propagatingdirection; a rotation-side transmission line, having an axiallysymmetrical electric field distribution or magnetic field distribution,arranged coaxially with the fixed-side transmission line so as to berotatable about an axis of the fixed-side transmission line; atransmission-line side choke disposed between the fixed-sidetransmission line and the rotation-side transmission line and arrangedto cause a short-circuit between the fixed-side transmission line andthe rotation-side transmission line at a high frequency; and a primaryradiator disposed in the rotation-side transmission line so as to berotatable together with the rotation-side transmission line forradiating high-frequency signals that have passed through therotation-side transmission line in parallel with a rotation axis of therotation-side transmission line in a manner that is not coaxial with therotation axis.
 12. The apparatus according to claim 11, furthercomprising a secondary radiator arranged on the line of the radiatingdirection of the primary radiator, the secondary radiator changing anoutgoing radiation direction in accordance with an incident position ofhigh-frequency signals.
 13. The apparatus according to claim 12, whereineach of the fixed-side transmission line and the rotation-sidetransmission line includes a circular waveguide having a propagationmode in a TM01 mode as the magnetic field distribution axiallysymmetrical about the propagating direction.
 14. A transmitter/receiverincluding the antenna apparatus according to claim
 12. 15. The apparatusaccording to claim 11, wherein each of the fixed-side transmission lineand the rotation-side transmission line includes a circular waveguidehaving a propagation mode in a TM01 mode as the magnetic fielddistribution axially symmetrical about the propagating direction.
 16. Atransmitter/receiver including the antenna apparatus according to claim15.
 17. A transmitter/receiver including the antenna apparatus accordingto claim 11.